Fasteners for attachment of drywall (gypsum board) to a metal substrate are, generally helically threaded round screw bodies or round nail shanks (center shanks). The center shanks of these type fasteners penetrate the top paper of the drywall paper-gypsum-paper laminate then the head countersinks into the top paper laminate to such a distance as to be flush or slightly below flush with the top surface. It is necessary for ultimate strength of drywall board fastening that the top paper laminate not be cut around the perimeter of the head. If this situation occurs it is not within building code specifications.
It has been discovered that the central shank of both types of conventional fasteners used for this application (screws and nails) cut this top paper laminate. This is obvious, but what is not obvious is that this allows the paper to stretch as the head countersinks. It is this stretching of the paper that allows the head perimeter to countersink into the gypsum without cutting through the top paper laminate. Additionally, the head of these fasteners are rounded on their edges to eliminate a sharp edge.
With current fasteners, heads are of either a cupped shape (nails) or are flat across the top while incorporating a driving recess (screws). The need for the cupped head for nails is to provide a reservoir to hold top finish coats (generally plaster). For screws, this reservoir is provided by the driving recess. The need for depression is to create an unequal mass in the fastener middle to hold the finish coat in place. The finish coat easily adheres to the paper along the perimeter of the fastener head. However, if the complete span of the head were flat without depression, the resulting finish coat would easily break-away with the slightest pressure. The problem with these depressions is that they hold an unequal mass of finish coat. As the water-based coating dries, the perimeter dries faster than the middle mass, this due to, in major part, the absorbtion characteristics of the top paper laminate. Drying time means waiting time for the installer to sand and finish the product. Unequal drying time means cracking in the finish coat in the middle, large mass area.
The present invention incorporates a structure to allow a fastener including an elongated flat body having a driving head disposed to one side thereof to properly countersink without tearing the top paper laminate and to allow for a more even finish coat, faster drying time and substantial reduction in cracking of the finish coat. Prior art patents to Flora (U.S. Pat. No. 2,751,052); Gombo (U.S. Pat. No. 2,382,474); Janke (U.S. Pat. No. 3,973,295); Enstrom (U.S. Pat. No. 3,882,755) and Fulton (U.S. Pat. No. 2,155,893) each disclose generally an “L” shaped fastener as above described but none deal with the problem of allowing the head to properly countersink into drywall.